U.S. Naval Observatory Alternate Master Clock

The U.S. Naval Observatory Alternate Master Clock at Schriever Air Force Base. It is used to check the time being distributed by the Global Positioning Satellites. The clock here showed 23:59:60 Saturday, January 1, 2006, reflecting the addition of the first leap second in seven years.

Caption:

The U.S. Naval Observatory Alternate Master Clock at Schriever Air Force Base.